Field of the Invention
The present invention relates to a method of manufacturing a thermochromic substrate, and more particularly, to a method of manufacturing a thermochromic substrate, by which the transmittance of the thermochromic substrate can be increased.
Description of Related Art
Thermochromism refers to the phenomenon in which an oxide or a sulfide of a transition metal undergoes a change in its crystal structure below and above a specific temperature (i.e. a transition temperature (Tc)), so that its physical properties (electrical conductivity and infrared (IR) transmittance) suddenly change.
When a glass is coated with a thin film that has such thermochromic capability, a “smart window” can be produced, which transmits visible light but blocks near infrared rays and infrared rays at or above a predetermined temperature in order to prevent the indoor temperature from increasing. The application of smart windows to vehicles or buildings may be very effective in saving energy. Materials that exhibit thermochromism include oxides of several transition metals, of which vanadium dioxide (VO2) is being studied since its transition temperature is 68° C., which is relatively close to a temperature at which practical application becomes possible.
Vanadium oxides, such as VO2, are present in the form of a variety of crystalline phases, such as V2O3, V3O5, V4O7, V6O11, V5O9, V6O13, V4O9, V3O7, V2O5 and VO2. The thermochromic characteristics appear only in the crystalline phase of VO2.
Therefore, in order to transform vanadium oxides that are present in a variety of crystalline phases, such as V2O3, V3O5, V4O7, V5O9, V6O11, V6O13, V4O9, V3O7, V2O5 and VO2, into VO2 in the crystalline phase, a method of heating a glass substrate to a high temperature and then coating the glass substrate with a vanadium oxide, a method of coating a glass substrate with a vanadium oxide, followed by post annealing, and the like are used.
However, the thermochromic thin film that is manufactured by the foregoing method exhibits the characteristics of metal and a resultant low transmittance of visible light, which are drawbacks.
In order to increase the transmittance of visible light, a method of decreasing the thickness of the thermochromic thin film can be used. However, this causes the problem in which the phase transition characteristic of the thermochromic thin film becomes nonuniform.
Therefore, a method of increasing the transmittance of visible light by forming a multilayer film structure, which includes a low-refractivity thin film and/or a high-refractivity thin film in addition to the thermochromic thin film, is used.
In this method of forming the multilayer film structure of the related art, the multilayer film structure is produced by forming a high- or low-refractivity thin film as an underlying layer, coating the high- or low-refractivity thin film with a VO2 thin film, and then coating the VO2 thin film with a high- or low-refractivity thin film.
However, when the multilayer film structure is manufactured by this method, the VO2 thin film is oxidized during the process of forming the multilayer film structure. Then, the VO2 undergoes phase change into a different crystalline phase of vanadium oxide, such as V2O3 or V2O5, which is problematic.
Specifically, when the high- or low-refractivity thin film formed as the underlying layer is coated with the VO2 thin film, oxygen diffuses in the underlying thin film in a high-temperature atmosphere, in which the VO2 thin film is formed as a coating. Consequently, the VO2 undergoes a phase change into a different crystalline phase of vanadium oxide.
In addition, when the VO2 thin film is coated with the high- or low-refractivity thin film, the VO2 thin film is exposed to oxygen in reactive sputtering, in which the high- or low-refractivity thin film is formed as a coating. The oxygen then diffuses into the VO2 thin film, and thus the VO2 undergoes phase change into a different crystalline phase of vanadium oxide.
Accordingly, when the multilayer film structure for increasing the transmittance of the thermochromic glass is formed by the method of the related art, oxygen diffuses into the VO2 thin film in the process of forming the multilayer film structure, and thus the VO2 undergoes a phase change, thereby losing its thermochromic characteristics.
The information disclosed in this Background of the Invention section is only for the enhancement of understanding of the background of the invention, and should not be taken as an acknowledgment or any form of suggestion that this information forms a prior art that would already be known to a person skilled in the art.